The present invention relates to an implant for implantation in, in particular, humans, which implant comprises flexible, thread-shaped elements and is particularly suitable for replacing ruptured articular ligaments. The implant is intended to be a temporary implant which disintegrates in time into fragments which are so small that they can be transported away by the blood and excreted through the kidneys.
Every year, millions of people are affected by damage to articular ligaments and tendons. A damaged ligament can be treated by surgical intervention or by conservative therapy. In spite of the fact that leading orthopaedic experts agree that surgical intervention is to be preferred in most cases, conservative therapy remains the most frequently used alternative. A major reason for this is that existing operative techniques using existing implants are considered to be inadequate.
A common feature of all types of reconstruction is that the surgeon has to use some form of replacement material to replace the damaged tissue. The most frequently used type of replacement material is tissue of the patient himself (autograft) which the surgeon takes from other parts of the body. This tissue is often supplemented with a synthetic material as reinforcement (augmentation implant). Alternatively, use is made of only a synthetic material (prosthetic implant). Implant materials which have been tried over the last 20 years in addition to autografts are inter alia tendons from animals (xenografts), deceased humans (allografts), synthetic materials in the form of non-degradable bands (Dacron, polyethylene, polypropylene, carbon fibres, polytetrafluoroethylene), and a degradable band made of polydioxanone.
Temporary implants for implantation in humans or animals comprising flexible, thread-shaped elements are previously known. One such has been described in Swedish patent specification 457692. The implant according to this patent specification consists of a bioresorbable material and is intended to replace completely or partly a tendon, a ligament or a cruciate ligament. The implant has an elongate shape and is flexible. Its main characteristic is that the structure has longitudinal grooves or ducts intended to serve as initial growth guides for new fibrous tissue. Furthermore, a large number of bioresorbable materials are also known and used for other types of implant.
In certain cases, the synthetic non-degradable implant materials have proved to have inadequate tissue-affinity and in the majority of cases inadequate elasticity with creep or fatigue failure as a consequence.
Biological tendon tissue from the patient himself, animals or deceased humans has not proved to be an optimum alternative either. The absence of a natural blood supply means that the elasticity and the strength are already reduced after a few weeks. Moreover, there is always a risk of transmitting infection when using implants from other humans and animals. In cases where tissue is taken from other parts of the body, the patient may suffer temporary or permanent harm from the wound created at the place from where healthy tissue has been taken.
It has therefore long been a requirement to produce a resorbable implant without the abovementioned shortcomings and, according to the following invention, a porous, in humans or animals biodegradable, biocompatible implant for implantation in humans or animals comprising flexible, thread-shaped elements has consequently been produced, which is characterized in that the thread-shaped elements consist of a number of thread bundles containing up to several thousand threads which in turn contain 50 to 500 filaments with a combined density of 5 to 120 tex, the thread bundles having a twist of 0 to 150 revolutions/meter and being held together by weft threads with a distribution density of a few threads per cm up to roughly 100 threads per cm calculated in the longitudinal direction of the thread-shaped element.
According to the invention, it is suitable for the weft threads to consist of the same type of thread as the other threads in the thread-shaped element.
According to the invention, the material in the threads should consist of a linear block polymer with a molecular weight of at least 104 Dalton, preferably at least 105 Dalton, comprising urea groups and urethane groups and also ester groups at such a distance from one another that, after hydrolysis of the same, fragments arise which are so small that they can be excreted from a human body, and also comprising primary NH2-end groups and/or OH-end groups which can be replaced by, for example, monoamines such as butylamine or ethylamine.
The implant according to the invention preferably consists of a central isotropic part for essentially absorbing constant loading, and a movable outer part for absorbing forces caused by extension and/or compression.
According to the invention, the implant consists of an articular ligament implant or tendon implant.